This study was designed to examine haemodynamic and haematologic effec
ts of the crown-of-thorns starfish venom (Acanthaster planci venom: AP
V) in dogs. Severe systemic hypotension, thrombocytopenia and leukopen
ia were induced by APV (1.0 mg protein/kg i.v.), followed by gradual r
eturn to the baseline level within 60 min. Hypotension was presumably
caused by two factors: an early decrease in systemic vascular resistan
ce and the large reduction in cardiac output due to reduced ventricula
r filling. Indomethacin, a cyclooxygenase inhibitor, remarkably suppre
ssed systemic hypotension induced by APV. The peak reduction in system
ic pressure was associated with concomitant rise of plasma 6-keto-PGF(
1 alpha), a major stable metabolite of prostacyclin. Thus, the hypoten
sive effect of APV may be caused primarily by prostacyclin and/or some
vasodilating prostaglandins. In contrast, thrombocytopenia and leukop
enia were not affected by cyclooxygenase inhibitor, 5-lipoxygenase inh
ibitor or platelet activating factor (PAF) receptor antagonist. When A
PV was administered repeatedly, tachyphylaxis was developed in haemody
namic effects, but not in haematologic effects. These findings suggest
that APV-induced hypotensive effects may occur mainly through endogen
ous production of vasodilating prostaglandins including prostacyclin,
although APV-induced thrombocytopenia and leukopenia may be caused by
other mechanism(s) unrelated to arachidonate metabolites and/or PAF.